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A raw image file contains minimally processed data from the image sensor of a Digital Camera or Image Scanner . Raw (as in not yet "cooked") files are so named because they are not yet processed and ready to use by a Bitmap Graphics Editor , Printed , or displayed by a typical web browser. The image must be processed and converted to an RGB format such as TIFF or JPEG before it can be manipulated. BENEFITS Nearly all digital cameras can process the image from the Sensor into a JPEG file using settings for White Balance , Color Saturation , Contrast , and sharpness that are either selected automatically or entered by the photographer before taking the picture. Cameras that support raw files save these settings in the file, but defer the processing. This results in an extra step for the photographer, so raw is normally only used when additional computer processing is intended. However, RAW permits much greater control than JPEG for several reasons:
DRAWBACKS Camera raw files are 2-6 times larger than JPEG files. Some raw formats do not use compression, some implement Lossless Data Compression to reduce the size of the files without affecting image quality and others use Lossy Data Compression where quantization and filtering is performed on the image data. This avoids or reduces the Compression Artifacts inherent in JPEG, but means that fewer images can fit on a given Memory Card . It also takes longer for the camera to write raw images to the card, so fewer pictures can be taken in quick succession (affecting the ability to take, for example, a sports sequence). The time taken in the image workflow is an important factor for choosing RAW instead of ready to be used formats. SOFTWARE SUPPORT Cameras that support raw files typically come with Proprietary Software for conversion of their raw format to TIFF or JPEG. Other conversion Programs and Plugin s are available from vendors that have either licensed the technology from the camera manufacturer or Reverse-engineered the particular raw format. A portable Open Source program, Dcraw , supports most raw formats and can be made to run on operating systems such as Unix not supported by most commercial software. Raw file formats are proprietary, and differ greatly from one manufacturer to another, and sometimes between cameras made by one manufacturer. In , Nikon , Sony and others include elements of Encryption designed to make it harder for others to decode the format. The Leica Digital Modul-R (DMR) was the first camera back to use DNG as its native format. Microsoft too is now including support for RAW, releasing thumbnail viewers, and it appears that they plan on embedding support into future versions of Windows. In 2005 , Apple Computer introduced several products which offered RAW file support. In January, Apple release IPhoto 5, which offered basic support for viewing and editing RAW files. In April, Apple introduced a new version of it's operating system, Mac OS X 10.4 Tiger , which added RAW support to Preview, it's PDF and image viewing application. Finally, in October, Apple released Aperture , a photo post-production software package for professionals whose chief feature is full support for RAW files. Picasa , a free image editing and cataloguing program from Google supports many raw formats. PROCESSING There is no single standard algorithm for converting data from a Bayer Filter or Foveon sensor into RGB format. Instead, a number of different algorithms have been proposed, and some have been patented in the USA. Thus, different programs are likely to give slightly different results, of better or worse subjective quality, for any particular image. RAW files are sometimes referred to as CCD-RAW (even for CMOS sensors). Although the term "raw" describes files in the classical sense of "raw data" vs. "cooked data", raw files typically are slightly processed in the camera. In general, this processing is limited to algorithms that require direct access to the camera's hardware. This includes "long exposure noise reduction" (aka "dark frame subtraction") and the mapping out of "hot" (too bright) or "dead" (too dim) pixels. It also often includes rudimentary Noise Reduction . Noise reduces the effectiveness of compression algorithms, so files are compressed more efficiently when noise reduction is applied before compression. SEE ALSO EXTERNAL LINKS
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